Edit the ON SCHEDULE clause under Schedule tab. The ON SCHEDULE clause determines when, how often, and for how long the SQL statment defined for the event repeats. This clause takes one of two forms:

AT
AT timestamp is used for a one-time event. It specifies that the event executes one time only at the date and time, given as the timestamp, which must include both the date and time, or must be an expression that resolves to a datetime value.

Use +INTERVAL to create an event which occurs at some point in the future relative to the current date and time.

EVERY
For actions which are to be repeated at a regular interval, you can use an EVERY clause which followed by an interval. (+INTERVAL is not used with EVERY.)

STARTS
An EVERY clause may also contain an optional STARTS clause. STARTS is followed by a timestamp value which indicates when the action should begin repeating, and may also use +INTERVAL interval in order to specify an amount of time "from now".

For example: EVERY 3 MONTH STARTS CURRENT_TIMESTAMP + 1 WEEK means "every three months, beginning one week from now".

ENDS
An EVERY clause may also contain an optional ENDS clause. The ENDS keyword is followed by a timestamp value which tells MySQL when the event should stop repeating. You may also use +INTERVAL interval with ENDS.

For Instance: EVERY 12 HOUR STARTS CURRENT_TIMESTAMP + INTERVAL 30 MINUTE ENDS CURRENT_TIMESTAMP + INTERVAL 4 WEEK is equivalent to "every twelve hours, beginning thirty minutes from now, and ending four weeks from now".